In general, the automotive industry has sought to form automotive assemblies that have both structural integrity and relatively low weight. For example, an instrument panel assembly of an automotive vehicle must exhibit sufficient structural integrity for supporting one or more peripheral components, such as air bag assemblies, steering columns, or other panel parts, and at the same time, should maintain a low weight to assist in lowering the overall weight for the vehicle.
Talc-filled TPOs have gained widespread use in automotive exterior applications, such as fascia, and other applications, requiring a balance of rigidity, impact resistance, at temperatures down to about −30° C., resistance to scratching and marring, and resistance to deformation, at temperatures of about 100° C. The flex modulus for these grades of TPOs is typically between about 100,000 and 200,000 psi, and the HDT is typically below about 110° C.
New materials have been developed for soft TPOs that can be used as an instrument panel (IP) skin in automobiles. These materials are designed to be thermoformed after either extrusion or calendaring. Once formed, these skins exhibit the required low gloss, low temperature impact resistance, scratch and mar resistance, and grain retention.
The thermoformed IP skins described above are placed over a structure made from polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) copolymer and urethane foam is injected in between the skin and structure to create a “soft-touch” instrument panel. PC/ABS has been chosen, despite its cost, because of its greater rigidity (typically 330,000-350,000 psi flex modulus), and its greater resistance to deflection under load at elevated temperatures (typically 120° C.-130° C.). Because the structure must also remain undamaged when a passenger side airbag deploys, the structure must also be able to survive an airbag deployment at −20° C., preferably −30° C.
Of continuing interest to the automotive industry is to replace the PC/ABS structure with lower cost polyolefin alternatives. Several polypropylene compositions are described in the following patents or applications. U.S. Pat. No. 6,759,475 describes a resin composition based on crystalline polypropylene, which includes: (a) 3-65 percent, by weight, of a component soluble in paraxylene of 23° C., (b) 35-97 percent, by weight, of a component soluble in paraxylene of 135° C., and insoluble in paraxylene of 23° C., and (c) 0-30 percent, by weight, of a component insoluble in paraxylene of 135° C. (for example, see abstract). The component (a), soluble in paraxylene of 23° C., is composed substantially of an elastomeric constituent (a1) having a content of styrene, or its derivative, in the range of 0-35 percent, by weight, and an intrinsic viscosity (η) in the range of 0.1-5 dl/g. The component (b), soluble is paraxylene of 135° C., and insoluble in paraxylene of 23° C., is composed substantially of a crystalline polypropylene constituent (b1) having an isotactic pentad proportion (mmmm) of 97 percent or higher, a molecular weight distribution (Mw/Mn) of 6 or higher, and a molecular weight distribution (Mz/Mw) of 6 or higher. The component (c), insoluble in paraxylene of 135° C., is composed substantially of a filler (c1).
U.S. Patent Application No. 2004/0044107 describes a propylene resin composition that has good molding abilities and a good balance of physical properties as well as a good appearance, lower gloss and scratch resistance. These compositions can be used for interior car parts (for example, see abstract). The polypropylene resin composition comprises the following components; a crystalline homopolypropylene having MFR of 500 to 3,000 g/10 min; a polypropylene consisting of a crystalline homopolypropylene and an ethylene-propylene copolymer rubber having 45 to 80 percent, by mass, of a ethylene content; a polypropylene, consisting of a crystalline homopolypropylene and an ethylene-propylene copolymer rubber having 25 percent, by mass, or more, to below 45 percent, by mass, of a ethylene content; and an ethylene-α-olefin copolymer rubber (for example, see abstract).
U.S. Pat. No. 6,660,797 describes a propylene-based composition for molded polypropylene resin articles, excellent in resistance to scratching and moldability, and well-balanced properties between high rigidity and high impact strength, and also provides a method for molding the above propylene-based composition, to provide high-performance industrial parts and automobile parts, and in particular automobile interior parts (for example, see abstract). An example propylene-based resin composition contains the following components (A) and (B), as described below (for example, see column 2, lines 14-49). Component (A) is a propylene-based resin composed of the following components (a1), (a2) and (a3); 90 to 40 weight percent: (a1) propylene/ethylene block copolymer, composed of 60 to 83 weight percent of crystalline propylene homopolymer component (a1-1 unit) and 17 to 40 weight percent of ethylene/propylene random copolymer component (a1-2 unit), containing 30 to 52 weight percent of ethylene, and having a weight-average molecular weight of 230,000 to 600,000; and having a melt flow rate (230° C., 2.16 kg) of 15 to 150 g/10 min, and number of gels of 100, or less, for those having a size of 50 μm, or more, in the molded article of 25 cm2 (area) and 0.5 mm (thickness); 100 weight parts; (a2) talc having an average particle size of 0.5 to 15 μm; 0 to 200 weight parts; (a3) ethylene/α-olefin copolymer rubber, containing 20 to 50 weight percent of α-olefin of 3 to 8 carbon atoms and having a melt flow rate (230° C., 2.16 kg) of 0.3 to 100 g/10 min; 0 to 20 weight parts. Component (B) is a propylene-based resin material, composed of the following components (b1) and (b2); 10 to 60 weight percent: (b1) propylene homopolymer or propylene/ethylene block copolymer, having a component insoluble in orthodichlorobenzene, at below 120° C., accounting for 8 weight percent or more of the component insoluble at below 100° C., when fractionated with orthodichlorobenzene as the solvent, and wherein the component insoluble, at below 100° C., has a weight-average molecular weight of 200,000 or more, and melt flow rate (230° C., 2.16 kg) of 0.3 to 70 g/10 min; 15 to 80 weight parts; and (b2) talc or wollastonite having an average particle size of 0.5 to 15 μm; 20 to 85 weight parts (for example, see column 2, lines 14-49).
Additional polypropylene compositions are described in U.S. Pat. No. 5,286,776 and U.S. Pat. No. 6,667,359. Other polyolefin compositions and fabricated articles, such as automotive parts, prepared from the same, are described in U.S. Publication Nos: 2005/0029692; 2004/0188885; and 2004/0094986. Additional propylene-based polymers and compositions are described in described in U.S. Publication No. 2005/0272858 (see also International Publication No. 2004033509), and U.S. Publication No. 2004/0122196. However, the compositions disclosed in these references, and those discussed above, are complex and costly due to the number of polymeric components in each composition and/or do not meet one or more desired rheological, mechanical or thermal properties of the inventive compositions described herein. Moreover, several of the compositions disclosed in these references require a polypropylene/(ethylene/polypropylene) heterophasic rubber, which is not advantageous for low temperature impact properties.
There is a continued need for low cost polyolefin compositions, simple in polymeric formulations, and which can be used to form manufactured parts, such as automotive parts, that have excellent mechanical and thermal properties. There is a further need for filled TPO compositions that can be used to form reinforced, light weight automotive parts, such as light-weight injection molded parts. There is also a need for such compositions that can be used to form automotive parts with improved high temperature and low temperature performance properties. These needs and others have been satisfied by the following invention.